Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct positions. During treatment, small orthodontic appliances known as brackets are often connected to anterior, bicuspid, and molar teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the brackets and the associated teeth to desired positions for correct occlusion. Typically, the ends of the archwire are held by appliances known as buccal tubes that are secured to a patient's molar teeth. The brackets, archwires, and buccal tubes are commonly referred to as “braces.”
The orthodontic treatment of some patients includes correcting the alignment of the upper dental arch, or maxillary jaw, with the lower dental arch, or mandible jaw. For example, certain patients have a condition referred to as a Class II malocclusion, or “overbite,” where the lower dental arch is located an excessive distance in a rearward direction relative to the location of the upper dental arch when the jaws are closed. Other patients may have an opposite condition referred to as a Class III malocclusion, or “underbite,” wherein the lower dental arch is located in a forward direction of its desired location relative to the position of the upper dental arch when the jaws are closed.
A number of approaches have been developed to treat Class II and Class III malocclusions. One of the most common approaches for treating a Class II malocclusion is to use an intra-oral orthodontic appliance known as a “Herbst” device. A conventional Herbst device is comprised of a sleeve and tube assembly. Typically, one component of the assembly is pivotally secured to a molar tooth in the upper arch, while another component is pivotally secured to a bicuspid or anterior tooth in the lower arch, or a cantilever arm in the lower arch. Oftentimes, both the sleeve and tube components are pivotally secured to an archwire, bracket, cap, or other orthodontic appliance associated with a particular tooth. Such a Herbst device is shown in U.S. Pat. No. 3,798,773 (1973), issued to Northcutt.
Herbst devices operate by forcing the lower arch into a desired occlusion position when the mouth is opened and closed. In other words, the Herbst devices prevent a patient from comfortably closing his or her mouth unless the lower arch is physically repositioned forward. If the arches are not repositioned, the sleeve of the Herbst device impacts a portion of the tube or an attachment connected to the tube so as to create a hard, fixed “stop” that is uncomfortable for the patient. To compensate for this uncomfortable stop the patient repositions their lower jaw forward. Eventually, the patient experiences muscular adaptation based upon a learned response such that the jaws begin to naturally close with the proper occlusion. Because Herbst devices were first developed in the early 1900's, their safety and reliability have been well documented.
Although Herbst devices have generally proven to be successful products, there are several concerns that limit their appeal and effectiveness. For example, Herbst devices are typically designed with long and stiff assemblies in order to withstand the significant forces exerted by the muscles of mastication. In addition to making the devices more noticeable within a patient's mouth, these large assemblies often create discomfort near the front of the mouth. Cheek muscles are relatively tighter around the anterior teeth than the posterior teeth and thus become easily irritated from tightly rubbing against the Herbst device.
Additionally, the anterior teeth have a tendency to flare or tip forward when they are connected to a Herbst device. While a conventional Herbst device may be used to correct a malocclusion at the same time that archwires and brackets are used to prevent this tipping, there are several significant challenges with doing so. Specifically, when the Herbst device extends from a molar on the upper arch to a bicuspid tooth or cantilever arm on the lower arch, the sleeve and tube assembly obstructs access to a large number of teeth. This obstruction makes it extremely difficult for practitioners to bond brackets to those teeth. Although some practitioners have attempted to circumvent this problem by welding extra parts onto the Herbst device or by placing the brackets in unusual positions, none of these ad-hoc approaches have proven to be a suitable solution.
As a result, many practitioners prefer to perform different treatment methodologies at different times. For example, a Herbst device may be used to correct a malocclusion prior to installing brackets for repositioning teeth. This separate treatment is undesirable to both the patient and practitioner because it not only increases the overall time that the patient must wear orthodontic appliances, but also increases the number of orthodontic modifications required to control the tipping of the anterior teeth.
For all these reasons, several attempts have been made to develop other suitable devices for correcting malocclusions. More specifically, several attempts have been made to develop a smaller intra-oral device that connects to the posterior teeth of a patient. As discussed above, the patient's cheek muscles are more relaxed at this rearward location in the mouth. Additionally, posterior teeth such as molars provide a good anchoring location for applying forces to move one jaw relative to the other jaw because of the relatively large size of their roots.
One such device is disclosed in U.S. Pat. No. 5,848,891 (1998), issued to Eckhart et al. and assigned to the Assignee of the present invention. The Eckhart device includes a first member mounted to a molar in the upper arch and a second member mounted to a molar in the lower arch. A buccally extending projection on the second member strikes an obstruction element on the first member when the lower jaw is closed in an uncorrected position. The obstruction element and buccally extending projection prevent complete closure of the upper and lower jaws unless the mandible is advanced sufficiently forward to enable the buccally extending projection to clear the obstruction element. Although such a disconnected system is relatively compact and does not interfere with braces or other orthodontic components, the contact between the obstruction element and the buccally extending projection provides only a limited range of correction. Furthermore, if the obstruction element and buccally extending projection do not make proper contact, these components may become engaged together and lock the upper and lower jaws.
Another type of intra-oral orthodontic device to treat Class II malocclusions includes one or more linkages having pivotal connections. These devices typically have a Z-shaped configuration and often incorporate a spring element to create a light, continuous force that enhances molar distalization. For example, U.S. Pat. No. 5,645,424 (1997), issued to Collins, Jr., discloses a central linkage having outer arms pivotally connected to the ends thereof. The outer arms are adapted to engage respective tubes on the molar teeth of the upper and lower dental arches. U.S. Pat. No. 5,980,247 (1999), issued to Cleary, discloses a related device having two linkages and three pivotal connections. U.S. Pat. No. 4,382,783 (1983), issued to Rosenberg, discloses a device having a configuration somewhat similar to the device of Cleary except that one of the linkages is a telescopic rod.
While the above-described devices have the advantages of a molar-to-molar connection, the increased number of parts and pivotal connections typically makes them more prone to breakage due to mastication forces. Additionally, many practitioners are hesitant to install such devices because their configurations differ significantly from traditional Herbst devices and therefore lack the extensive historical data and experience associated with traditional Herbst devices.
As can be appreciated, there is a need in the orthodontic art for improved devices for repositioning the jaws of patient with a Class II malocclusion. Devices are needed that function reliably and efficiently and yet are not prone to breakage or likely to cause adjacent orthodontic components to be detached from the associated teeth.